Foods are changed slowly by various kinds of fungi existing in air. In order to slow down the speed of change of foods, besides a method using refrigerator, a vacuum-storing method has been used, in which air in the container is removed, making the pressure lower inside than outside. Prior arts about vacuumed container used in the vacuum-storing method include Korean Application Publications 10-2008-0014536 (Title: Multi-purpose Vacuum Container Lid) and 10-2010-0078576 (Title: Vacuum Container Lid and Check Valve and Packing for the Same).
According to vacuumed containers disclosed by the two prior arts, air in the internal space of the container escapes outwards through a check valve provided in a container lid by pressure (external force) applied when disposing a packing at the opening part of the container and covering with the container lid, and if the external force is removed in such a state, the volume of the internal space of the container gets larger due to the packing's elasticity, but since the check valve shuts down external air entering into the inside of the container, a vacuum mood of lower than the atmosphere is made in the internal space of the container. According to such a vacuum-making structure, the pressure difference between the inside and outside of the container maintains the container lid stuck to the opening part of the container main body. Since the pressure difference is large, it is very hard for a person to detach the container lid from the container main body forcefully unless the check valve is opened forcefully. Since the locking function of the container lid is obtained using such pressure difference between the inside and outside of the container, and in order to avoid a structural complexity, any separate locking means was not provided.
However, it was found through actual usage that the following improvements are needed for the locking function using the pressure difference between the inside and outside of the container. Even though packing or check valve is made with silicon or rubber with excellent sealing function, since they cannot provide a perfect sealing, as time goes on, the pressure difference between the inside and outside of the container gets smaller and smaller, and the locking force of the container lid with respect to the container main body is weakened accordingly, so that sometimes it falls in a state, in which when pull up the container lid it get detached easily from the container main body. If the container is used constantly without washing completely, small debris (food scraps, etc.) may be stuck between the packing or check valve and a surface of the container, and then sealing can be damaged due to such a portion with debris. In such a case, weakening of pressure difference may speed up. In cases, the user tampers the check valve and external air may be introduced into the container, resulting in a similar situation. In such a state, if the user thinks that the container lid is attached strongly to the container main body and takes it out of the refrigerator, for example, by holding the container lid only, the container lid can be detached from the container main body by giving in to the weight of the container main body and contents in it. In such a case, the container main body can be toppled right away, or falls down after being lifted for a short while, pouring out the contents undesirably. If, when carrying food in the container for a picnic, the locking of container lid is weakened due to the above weakening of pressure difference, liquid contents may ooze out of the container when there is shaking or tilting.
On the other hand, there are various kinds of containers for food such as bowl-type or plate-type. Also, the shapes of container are diverse. In a case of bowl-type container, there is a shape, in which a side wall of the container is perpendicular to a bottom floor or more and more inclined outwards as approaching an opening part. In a case of plate-type container, the edge of opening part is nearly horizontal. Almost all the cases, such conventional containers do not have any structure having separate locking protrusions for engaging with a vacuum-sealed container lid. It is necessary to improve lids of such vacuum-sealed containers so as to engage stably with such vacuum-sealed containers without separate locking protrusions, preventing the contents from spilling.